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These aren't stars — they're galaxies. (NASA/ESA)
This photo, taken by the Hubble telescope, has been making the rounds since it was released yesterday. It's not hard to see why: the distant cluster of galaxies pictured looks coincidentally like a smiley face.
It's a pretty cute image. But the scientific truth about what's going on is far more fascinating.
Let's start with the eyes. They're not stars, but entire galaxies — groups of 100 billion or more stars packed together, like our Milky Way. These galaxies are so large that traveling across them at the speed of light would take you hundreds of thousands of years or more. And each of these stars, astronomers now believe, likely has a planet orbiting it. It's very possible that among the hundreds of billions of planets in each of those eyes, there's some form of alien life.
The curves that make up the face's edges and smile, meanwhile, are the result of a phenomenon called gravitational lensing. We're not looking at a curved light source, but at light that's coming from far behind the galaxies and is traveling through spacetime that's bent by the enormous gravitational pull of them, as shown in the simulation at right (via Urbane Legend)
The particular ring-like phenomenon in the picture, called an Einstein ring, occurs when the light source, the galaxies, and the viewer all line up directly. In essence, the galaxy eyes are acting as a magnifying glass, blowing up the light coming from behind them.
Billions of stars, in galaxies so huge that they bend spacetime itself. But most of us (this author included) can't look at the image without seeing a lopsided smile. As Rachel Feltman points out, this is due to a phenomenon called pareidolia: the inexplicable human tendency to see human faces in everything.
